the middle finger gesture started as far back as the middle ages. It was because archers (if I spelt it wrong big fucking deal) when captured got their middle fingers cut off. So enemy soilders walking by would give them this gesture showing they still had theirs. The middle finger was used for accuracy in shooting one.

2.can be a strange, friendly greeting for some. Alternative to "hello"

Example 1. You telling us to be quiet because of exams hay....here! TAKE THAT
(Gives The Finger)

Example 2. notices friend in distance.AAYY!!...Gives The Finger, sometimes accompanied with wavelike movements - like you wave your open hand when using the more traditional "hello"
why some consider this is a greeting, no-one will ever know

The finger is often nicknamed the middle finger or pulling the bridge. Raising the middle finger, the longest one, is a physical gesture saying, 'Fuck you!' or 'Fuck off!' or anything along those lines. AVGN does that out of frustration and anger, as his name implies.

Although the bow and arrow stories are nice they are incorrect. The finger was originated by an English king who used to make the gesture to potential brides, meaning 'would you like me to fuck you?'. He would do this to see their reactions. The middle finger and the wrist would move almost as a signal to come closer. This gesture became popular among all and was used jokingly.